A diesel engine achieves combustion by injecting fuel that vaporizes into the hot air of an engine cylinder. However, during cold starting conditions, the air loses much of its heat to the cylinder walls making engine starting difficult. For example, if fuel is injected into the cylinder too quickly, the heat required to vaporize the cold fuel reduces the air temperature about the injection point and may prevent or quench combustion. Thus, it is desirable to inject fuel slowly to disperse the fuel throughout the combustion chamber to evenly distribute the resulting heat losses in order to cause combustion.
The injection rate of hydraulically-actuated fuel injector systems, similar to those described in U.S. Pat. Nos. 5,191,867 and 5,181,494, is controlled by the actuating fluid pressure and viscosity. However, the fluid viscosity changes in response to fluid temperature and fluid grades. Therefore, it is desirable to control the actuating fluid pressure as a function of the fluid temperature and grade.
The present invention is directed to overcoming one or more of the problems as set forth above.